US4742224A - Charged particle energy filter - Google Patents

Charged particle energy filter Download PDF

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Publication number
US4742224A
US4742224A US06/944,451 US94445186A US4742224A US 4742224 A US4742224 A US 4742224A US 94445186 A US94445186 A US 94445186A US 4742224 A US4742224 A US 4742224A
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United States
Prior art keywords
plates
base plate
plate
stack
holes
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Expired - Lifetime
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US06/944,451
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English (en)
Inventor
Steven Chu
Aly Dayem
Eric H. Westerwick
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AMERICAN TELEPHONE AND TELEGRAPH Co AT&T BELL LABORATORIES
AT&T Corp
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AMERICAN TELEPHONE AND TELEGRAPH Co AT&T BELL LABORATORIES
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Priority to US06/944,451 priority Critical patent/US4742224A/en
Assigned to AMERICAN TELEPHONE AND TELEGRAPH COMPANY, BELL TELEPHONE LABORATORIES, INCORPORATED reassignment AMERICAN TELEPHONE AND TELEGRAPH COMPANY ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: CHU, STEVEN, DAYEM, ALY, WESTERWICK, ERIC H.
Priority to DE19873742197 priority patent/DE3742197A1/de
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/44—Energy spectrometers, e.g. alpha-, beta-spectrometers
    • H01J49/46—Static spectrometers
    • H01J49/48—Static spectrometers using electrostatic analysers, e.g. cylindrical sector, Wien filter

Definitions

  • This invention relates to charged particle energy filters, and more particularly to devices capable of selecting only charged particles having energies within a relatively narrow range of energy.
  • Secondary Ion Mass Spectroscopy is a surface analysis technique that characterizes materials by determining the mass of the secondary ions that are made to leave the material. To achieve maximum mass resolution, only those secondary ions having energies within a relatively narrow range must be allowed to enter the mass analyzer. See the article entitled “New wide angle, high transmission energy analyzer for secondary ion mass spectrometry", by M. W. Siegel and M. J. Vasile, Rev. Sci. Instrum., 52(11), November 1981, pp. 1603-1615.
  • a shaped resistive disk is used to establish the potential distribution proportional to 1/r.
  • This resistive disk is made of a ceramic material impregnated with metal particles.
  • this impregnated ceramic material is porous and hence incompatible with ultrahigh vacuum applications. It has a poor electrical performance attributable to its nonuniform resistivity and the random localized charging of its surface.
  • the present invention is based on the idea that the potential distribution can be segmented into a number of equipotential concentric rings, and those rings need not be coplanar, provided the potentials applied to them obey the relationship V ⁇ (1/r).
  • the problem of providing an ion energy filter with an improved electrical performance in a SIMS chamber is solved in accordance with the present invention wherein a plurality of circular conductive plates, each one of which has a centrally positioned hole of a different size from all of the other plates, are assembled to each other and to a base plate so as to form a stack wherein each plate is electrically insulated from all of the other plates.
  • the base plate has a conductive hemispherical structure mounted at its center and all of the plates, where needed, have two holes diametrically positioned a predetermined distance from the center through which the ions can pass.
  • Each plate also has a tab which is connected to a different junction in a series of resistors.
  • FIG. 1 is a pictorial drawing of an ion energy filter constructed in accordance with the present invention
  • FIG. 2 is a cross-sectional view of the ion energy filter shown in FIG. 1;
  • FIG. 3 is a balloon diagram of the ion energy filter in the region of one of the assembly bolts
  • FIG. 4 is a top view of the base plate used in the ion energy filter
  • FIG. 5 is a top view of a representative one of the plates used in the ion energy filter.
  • FIG. 6 is a top view of the top ring of the ion energy filter.
  • An ion energy filter can be constructed in accordance with the present invention by fabricating 19 thin stainless steel plates of the type shown in FIG. 5.
  • Each plate has a central hole with a unique inside radius.
  • Each plate 500 has a tab 520 located at a unique place on the circumference of the plate. As the central hole size is increased, the position of the tab is moved counterclockwise when the plates are viewed from the top.
  • An ion energy filter employing this set of plates can be constructed by fabricating a stainless steel base plate 400 of the type shown in FIG. 4.
  • a metallic hemisphere 230 is bolted to the center hole 430 of the base plate as shown in FIG. 2.
  • a ceramic tube 271 is placed in each of the counterbored holes 403 through 410.
  • a flat Teflon washer 311 is placed around each of the eight ceramic tubes and adjacent to the base plate 400.
  • a plate 500 of the type shown in FIG. 5 having the smallest central hole is positioned above the eight ceramic tubes. The plate is oriented so that the holes 501 and 502 align with the base plate holes 401 and 402, and the tab 520 is adjacent to the base plate opening 420.
  • the plate is then further positioned to align the eight holes 503 through 510 with the eight ceramic tubes.
  • the plate is made to slide down the ceramic tubes until it contacts the eight Teflon washers.
  • the installation of alternating layers of Teflon washers and plates is continued until all 19 flat plates are installed.
  • the plates are installed in the order of increasing central hole size.
  • a final set of Teflon washers is installed followed by the top ring 600 of the type shown in FIG. 6, which has counterbored holes 603 through 610 which accept the ceramic tubes as shown in FIG. 2 for two of the tubes.
  • a ceramic shoulder washer 272 is placed around each of eight 0-80 machine screws 261.
  • the machine screws 261 are inserted into the base plate holes 403 through 410 from the underside of the base plate.
  • the screws are guided by the ceramic tubes to the threaded holes 603 through 610 in the Top ring 600.
  • the screws are threaded into these holes and tightened until the Teflon washers are compressed to their nominal thickness.
  • the assembled stack can be represented by the cross-sectional drawing in FIG. 2.
  • the tabs 520 on the plates 500 form a counterclockwise spiral of evenly spaced tabs as shown in FIG. 1.
  • a resistor is welded between each of the adjacent tabs. Resistors are also connected between the lowest flat plate 500 and the base plate, and between the highest flat plate 500 and top ring 600. All resistors have the same value of resistance.
  • a wire is connected to base plate 400, and another wire is connected to top ring 600. When these wires are connected to a voltage source, the resulting current flowing through the chain of equivalent resistors produces potential steps of equal value of the set of plates.
  • an insulating disc 241 is secured to the underside of the base plate 400.
  • a metallic cap 242 is in turn secured to the insulating disc (refer to FIG. 2).
  • the disc and cap each have a hole on center of a diameter significantly larger than that of hole 401 in the base plate 400.
  • the insulating disc 241 and metallic cap 242 are centered at the axis of the hole 401, and are of such diameters as to not interfere with the hole 402, the entrance aperture of the ion energy filter.
  • the energy filter is to be used in an environment having strong ambient electromagnetic fields, these fields may interfere with the fields produced by the filter.
  • a large metallic outer hemisphere centered with the small metallic hemisphere 230 can be secured to the beveled rim of the top ring 600.
  • a small hole must be placed in the outer hemisphere to allow the entrance of the primary ion beam. The center of this hole must be on the axis of the energy filter entrance aperture defined by holes 402 and 502.
  • Each resistor 150 is fabricated by winding a resistance wire (having a composition of 73 percent Ni, 20 percent Cr, and 7 percent miscellaneous metals such as Al and Fe) onto a solid ceramic body to achieve a resistance of 503 ohms.
  • a resistance wire having a composition of 73 percent Ni, 20 percent Cr, and 7 percent miscellaneous metals such as Al and Fe
  • the resistance ranged from 502 to 505 ohms with a ⁇ 20 ppm/degrees C. temperature coefficient.
  • Copperweld leads having steel wires with a 40 percent conductive copper plating were secured to each end of the ceramic body to provide a means of external connection to the resistance wire.
  • the ion energy filter is composed of a stack of 20 thin metal plates, each insulated from the others and each having a centrally located hole with a unique radius.
  • the plate closest to the plane of the origin of the hemispherical field provided by metallic hemisphere 230 on the base plate 400 has the hole with smallest radius.
  • the radii of the holes in the subsequent plates increase with increasing distance from the origin.
  • the relative potential of each plate is determined by a chain of 20 resistors, with each junction connected to a plate. When a direct current is passed through the resistor chain, potentials are developed at each junction, and therefore on each plate.
  • each plate has a tab which extends beyond the outside diameter of the generally circular plate and is positioned such that when the plates are assembled to form a stack, the tabs occur at equal intervals on the circumference of the stack. This permits the resistor leads to be fastened from tab to tab, greatly simplifying the wiring. Only two wires (the ends of the resistor chain) are required to power the filter.
  • the two diametrically opposed apertures are positioned in the stack of plates and in the base plate below them (by holes 401 and 402) to permit the entrance and exit of secondary ions.
  • One of the apertures serves as an entrance aperture and the other serves as an exit aperture.
  • these apertures act as lenses.
  • the center hemisphere 230 is biased at the filters maximum negative potential. Because hemisphere 230 is mounted directly on base plate 400, and the material sample being analyzed is positioned just beneath the entrance aperture in this plate, the positive ions leaving the sample are accelerated into the entrance aperture of the base plate. This increases the secondary ion collection efficiency of the filter.
  • ions As the ions continue on their paths to the interior of the filter, they must pass through the entrance aperture provided by the holes in the plates. Each plate that they pass is biased less negatively than the preceding plate. The ions, therefore, experience a deceleration. The effect of this deceleration is to launch the ions into the central force field of the filter at the energies required for near circular orbits.
  • the selected ions approach the exit aperture of the plates, they are accelerated out of the filter by the increasingly negative potentials on the plates and the base plate.
  • the ions travel between the base plate and the quadrupole mass analyzer, they experience a deceleration because of the large negative potential on the base plate relative to the virtual ground of the quadrupole axis. This deceleration is necessary for proper mass analysis.
  • the resistors may be fabricated with unequal values and the radii of the central holes in the plates adjusted accordingly to continue to achieve a potential distribution which is proportional to the reciprocal of the radial distance from the center.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Electron Tubes For Measurement (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
US06/944,451 1986-12-22 1986-12-22 Charged particle energy filter Expired - Lifetime US4742224A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US06/944,451 US4742224A (en) 1986-12-22 1986-12-22 Charged particle energy filter
DE19873742197 DE3742197A1 (de) 1986-12-22 1987-12-12 Energiefilter fuer geladene partikel

Applications Claiming Priority (1)

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US06/944,451 US4742224A (en) 1986-12-22 1986-12-22 Charged particle energy filter

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DE (1) DE3742197A1 (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5008535A (en) * 1988-09-02 1991-04-16 U.S. Philips Corporation Energy analyzer and spectrometer for low-energy electrons
WO1993010554A2 (en) * 1991-11-12 1993-05-27 Fisons, Plc Charged particle energy analyser
US5557178A (en) * 1994-11-01 1996-09-17 Cornell Research Foundation, Inc. Circular particle accelerator with mobius twist
US20110266428A1 (en) * 2010-04-29 2011-11-03 Battelle Energy Alliance, Llc Apparatuses and methods for generating electric fields

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2640948A (en) * 1950-09-21 1953-06-02 High Voltage Engineering Corp Apparatus for utilizing a beam of high energy electrons in sterilization and in therapy
US3582649A (en) * 1968-10-21 1971-06-01 Varian Associates Retarding field electron diffraction spectrometer having improved resolution
US4126781A (en) * 1977-05-10 1978-11-21 Extranuclear Laboratories, Inc. Method and apparatus for producing electrostatic fields by surface currents on resistive materials with applications to charged particle optics and energy analysis
US4224518A (en) * 1978-12-21 1980-09-23 Varian Associates, Inc. Multistage cylindrical mirror analyzer incorporating a coaxial electron gun
JPS57194446A (en) * 1981-05-22 1982-11-30 Shimadzu Corp Charged particle energy analyzer
JPS59123154A (ja) * 1982-12-29 1984-07-16 Shimadzu Corp 飛行時間型質量分析装置
EP0208894A2 (de) * 1985-07-10 1987-01-21 Bruker Analytische Messtechnik GmbH Flugzeit-Massenspektrometer mit einem Ionenreflektor

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2640948A (en) * 1950-09-21 1953-06-02 High Voltage Engineering Corp Apparatus for utilizing a beam of high energy electrons in sterilization and in therapy
US3582649A (en) * 1968-10-21 1971-06-01 Varian Associates Retarding field electron diffraction spectrometer having improved resolution
US4126781A (en) * 1977-05-10 1978-11-21 Extranuclear Laboratories, Inc. Method and apparatus for producing electrostatic fields by surface currents on resistive materials with applications to charged particle optics and energy analysis
US4224518A (en) * 1978-12-21 1980-09-23 Varian Associates, Inc. Multistage cylindrical mirror analyzer incorporating a coaxial electron gun
JPS57194446A (en) * 1981-05-22 1982-11-30 Shimadzu Corp Charged particle energy analyzer
JPS59123154A (ja) * 1982-12-29 1984-07-16 Shimadzu Corp 飛行時間型質量分析装置
EP0208894A2 (de) * 1985-07-10 1987-01-21 Bruker Analytische Messtechnik GmbH Flugzeit-Massenspektrometer mit einem Ionenreflektor

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
Rev. Sci. Instrum, 52(11), Nov. 1981, "New wide angle, high transmision energy analyzer for secondary ion mass spectrometry" M. W. Siegel et al., pp. 1603-1615.
Rev. Sci. Instrum, 52(11), Nov. 1981, New wide angle, high transmision energy analyzer for secondary ion mass spectrometry M. W. Siegel et al., pp. 1603 1615. *

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5008535A (en) * 1988-09-02 1991-04-16 U.S. Philips Corporation Energy analyzer and spectrometer for low-energy electrons
WO1993010554A2 (en) * 1991-11-12 1993-05-27 Fisons, Plc Charged particle energy analyser
WO1993010554A3 (en) * 1991-11-12 1993-06-24 Fisons Plc Charged particle energy analyser
EP0713244A1 (de) * 1991-11-12 1996-05-22 FISONS plc Grundplatte für einen Energieanalysator für geladene Teilchen
GB2300066A (en) * 1991-11-12 1996-10-23 Fisons Plc Charged particle energy analyser
GB2300066B (en) * 1991-11-12 1997-03-19 Fisons Plc Charged particle energy analyser
US5557178A (en) * 1994-11-01 1996-09-17 Cornell Research Foundation, Inc. Circular particle accelerator with mobius twist
US20110266428A1 (en) * 2010-04-29 2011-11-03 Battelle Energy Alliance, Llc Apparatuses and methods for generating electric fields
US8502159B2 (en) * 2010-04-29 2013-08-06 Battelle Energy Alliance, Llc Apparatuses and methods for generating electric fields

Also Published As

Publication number Publication date
DE3742197A1 (de) 1988-06-30
DE3742197C2 (de) 1990-06-07

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